Try to fix intermittent failure in `handle reading ranges with missin…

…g/invalid "Content-Range" header` unit-test (PR 19114 follow-up)

Implements mozilla#19114 (comment), which didn't seem necessary at the time since the unit-tests passed (many times) in PR 19114.

test/webserver.mjs

@@ -189,7 +189,7 @@ class WebServer {
     if (this.verbose) {
       console.log(url);
     }
-    this.#serveFile(response, localURL, fileSize);
+    this.#serveFile(response, localURL, url.searchParams, fileSize);
   }
 
   async #serveDirectoryIndex(response, url, localUrl) {
@@ -287,7 +287,7 @@ class WebServer {
     response.end("</body></html>");
   }
 
-  #serveFile(response, fileURL, fileSize) {
+  #serveFile(response, fileURL, searchParams, fileSize) {
     const stream = fs.createReadStream(fileURL, { flags: "rs" });
     stream.on("error", error => {
       response.writeHead(500);
@@ -304,6 +304,12 @@ class WebServer {
       expireTime.setSeconds(expireTime.getSeconds() + this.cacheExpirationTime);
       response.setHeader("Expires", expireTime.toUTCString());
     }
+
+    // Support test in `test/unit/network_spec.js`.
+    if (searchParams.has("test-network-break-ranges")) {
+      // Refer to the comment in `redirectHandler` below.
+      response.setHeader("Cache-Control", "no-store,max-age=0");
+    }
     response.writeHead(200);
     stream.pipe(response);
   }